A problem common to all semiconductor processing is contamination of structures formed on substrates. As those skilled in the art will appreciate, as geometries shrink and the complexity and functionality of circuitry on a given substrate increases, the problem of contamination becomes more acute. Sources of contamination for such structures include foreign materials present in the treatment chamber, foreign materials introduced via the plasma or treatment atmosphere, and contaminants introduced from the material being utilized in the treatment of the substrate, or being deposited thereon, or a precursor of such material.
Carbon is a contaminant typically encountered in semiconductor processing where an organic source, i.e. a precursor material, or treatment material is utilized. For example, where ultrathin semiconductor films are deposited by various art-recognized techniques from gaseous organic precursors, carbon is frequently present in the resultant films, regardless of the precautions taken. In such deposition techniques, the precursor(s) react, typically at an elevated temperature or in an RF plasma, to deposit the desired material. It is intended that the carbon present will form volatile by-products, e.g. carbon dioxide and carbon monoxide that can be evacuated from the reaction chamber. However, some of the precursor, and/or carbon-containing reaction products, inevitably become entrapped in the film as it is being deposited. It is essential that these contaminants be removed efficiently and without adverse effect to the film or the underlying semiconductor structure.
The problem of carbon contamination is particularly acute when the film being deposited is a dielectric material intended to function as a gate dielectric or insulator in such art-recognized applications as: alternate gate dielectric to replace the thermally grown silicon dioxide on silicon for CMOS; inter-poly dielectric for Flash memory; capacitor dielectric for DRAMS, linear capacitors for analog applications, e.g. microwave applications, and the like. Gate dielectrics in such applications, which can be as thin as 10-50 Angstroms, are especially susceptible to contamination. In such instances, the presence of carbon, including conductive carbon, will change the properties, e.g. conductivity, of the dielectric thus adversely affecting its ability to function as a gate dielectric or in memory applications. It will be appreciated that, the thinner the deposited film, the greater the sensitivity to changes in conductivity as a result of carbon contamination.
The major problem caused by the presence of carbon in thin film gate dielectrics is the formation of silicon monoxide. In applications such as discussed above, the gate dielectric, generally a metal oxide or silicon dioxide, is typically deposited directly onto silicon or polysilicon. In the vertical fabrication of semiconductor structures, because the deposited layers of material are so thin, one of the most critical requirements is that the surfaces of deposited layers be smooth. Carbon as an impurity is particularly detrimental at or near the interface of silicon and the oxide. Regardless of whether the silicon is amorphous, polycrystalline or single crystal, the carbon catalyzes the formation of silicon monoxide which is volatile due to its low vapor pressure. The volatilization of silicon monoxide from the silicon/oxide interface causes the silicon surface to become rough which can materially impact both performance and reliability of the resulting device. This can take place not only during deposition, but during subsequent annealing/densification treatments as well.
Those skilled in the art will appreciate that, although the requirements of smoothness and uniformity for any material deposited onto the surface of a semiconductor substrate in the construction of VLSI circuitry are stringent, those for gate dielectric material are particularly so since the integrity of gate dielectric materials is essential to the performance and reliability of the device. Therefore, surface roughness of the substrate, particularly where an overlying dielectric may not have optimum covering capacity, can significantly degrade both performance and reliability of devices formed therefrom.
There are several art-recognized techniques for preventing or minimizing carbon contamination in semiconductor dielectric films. Perhaps the most common is simply to raise the temperature in the reaction chamber, thus enhancing the formation of volatile carbon compounds, primarily carbon monoxide and carbon dioxide, which can be evacuated from the chamber. This solution, however, cannot be utilized when it is desired to deposit a dielectric film from an organic precursor at low temperatures. Another significant limitation to this solution is that the temperature cannot be raised above the pyrolysis temperature of the organic precursor since that would significantly raise the amount of carbon contamination in the film. Another common technique is to remove the carbon contaminant post-deposition of the dielectric film by high-energy processes, such as the generation of in-situ plasmas and in-situ ion bombardment of the film. These processes, which typically also cause the formation of carbon monoxide and carbon dioxide, are not suitable for all situations where it is desired to remove carbon contamination, particularly where the substrate contains structures that are not sufficiently robust to withstand such high energy treatment. Again, as the size and thickness of films deposited on a semiconductor substrate shrink, so do the possible applications of such high-energy treatments to remove carbon contamination.
Hence, it will be appreciated that there is a need for an efficient process for the deposition of gate dielectric or other similar materials from an organic precursor at low temperatures wherein the deposited film can be rendered substantially free of carbon contamination without resorting to conventional procedures that could have a negative effect on the performance or reliability of devices formed therefrom. The exponential growth of the semiconductor industry can only be sustained if high dielectric constant(K) materials can be developed for applications such as those discussed above. Such materials are provided in accordance with the present invention.